The present invention relates to flavour/aroma materials and the preparation of such materials and key intermediates. It is particularly (though not exclusively) concerned with vanilla flavour materials and related materials.
Supplies of natural vanilla bean extracts suffer from shortages of supply and variability in quality. Despite a wide range of natural flavour chemicals having become commercially available over the last 10-15 years, no entirely satisfactory natural vanillin flavour chemical product or vanilla flavour has yet been developed. The main difficulties in developing a cost-effective vanillin product are firstly the unavailability of the preferred raw material, ferulic acid; and secondly the difficulty in finding microbial strains that can accumulate vanillin due to its ease of further metabolism, for instance to vanillic acid, and its inhibitory effect on the metabolism of cells. The main difficulty in developing a natural vanilla flavour is the large number of different chemicals that together contribute to the superior flavour and aroma of vanilla bean extracts. In addition for the minor usage of vanilla in fragrances a colourless solid product is required rather than the coloured ethanol-water vanilla bean extracts.
Our earlier application WO-A-96/39859 discloses the production of some phenolic materials by the enzymatic hydrolysis of plant materials. Thus ferulic acid (la) was produced by enzyme treatment of wheat germ or wheat bran. Caffeic acid (1b) was produced by enzyme treatment of sunflower meal. Ferulic acid and esters thereof are valuable as precursor compounds and also as ingredients of foods and cosmetics, e.g. serving as antioxidants. 
Various workers have reported the microbial conversion of ferulic acid (1a) into vanillin (3) either directly (e.g. DE-A-19532317) or via vanillic acid (2) (FR-A-2724394).